What Do Valves Do?

Valves regulate fluid flow by varying the size of the flow passage. They can completely stop flow, throttle flow to a required rate, prevent back flow, and regulate pressure. Proper valve selection is essential because the wrong valve can cause inefficient operation, increased maintenance, or unexpected failure.

Valves can be operated manually with handwheels, levers, or gears, or automatically actuated by pneumatic, hydraulic, or electric actuators that respond to process signals for automatic control.

Common Types of Valves

1. Gate Valves

Gate valves are designed to fully open or fully close flow, typically used for on-off control where the valve doesn't need frequent operation. The gate lifts completely out of the way when open, creating very little flow resistance. They're commonly used in water supply systems and oil pipelines.

2. Ball Valves

Ball valves use a rotating ball with a hole through the center to control flow. When the hole aligns with the pipe, flow passes through; rotating the ball 90 degrees closes the valve. Ball valves are durable, provide tight shutoff, and open/close quickly, making them popular for many industrial applications.

3. Butterfly Valves

Butterfly valves use a rotating disc mounted on a spindle to control flow. They're lightweight, compact, and relatively inexpensive compared to larger valve types, making them popular for large diameter piping systems.

4. Check Valves

Check valves allow flow to move in only one direction, preventing back flow that could damage equipment or disrupt processes. They're found in virtually every piping system from domestic water to chemical processing.

5. Control Valves

Control valves automatically regulate flow rate or pressure based on a control signal from a process controller. They continuously modulate flow to maintain setpoints in industrial processes.

Selection Criteria

Choosing the right valve depends on several factors:

• Fluid Type: Corrosiveness, viscosity, abrasiveness, and temperature affect material selection (brass, cast iron, stainless steel, special alloys).
• Pressure Rating: The valve must safely withstand the maximum system pressure.
• Flow Requirements: What's the required flow rate? Is it on-off control or throttling?
• Actuation: Manual, pneumatic, hydraulic, or electric actuation based on process automation needs.

Maintenance and Service

Proper maintenance extends valve service life:

• Regular cycling of infrequently used valves prevents them from seizing
• Check packing glands and seals for leaks and adjust as needed
• Replace worn actuators and seals before they fail
• For automated valves, calibrate the positioner periodically to maintain accurate control